Lay Cheated Justice
A dead person can't be convicted of a crime, so the entire legal case, indictment, trial and conviction, will be erased from the record. Which really makes sense, since a dead person also can't appeal a conviction.
But that doesn't necessarily mean that his ill-gotten gains are untouchable. His estate can be sued civilly, which the SEC is in the process of doing. Though Lay's conviction can't be used in a civil case, since the conviction no longer exists, the testimony can be used.